Process to prepare a lubricating base oil

ABSTRACT

Process to prepare two or more base oil grades, which base oil grades having different kinematic viscosity&#39;s at 100° C. from a waxy paraffinic Fischer-Tropsch product having a content of non-cyclic iso-paraffins of more than 70 wt % by (a) obtaining from the waxy paraffinic Fischer-Tropsch product a distillate fraction having a viscosity corresponding to one of the desired base oil products, (b) performing a catalytic dewaxing step using the distillate fraction obtained in step (a) as feed, (c) separating the lower boiling compounds from the dewaxed product obtained in step (b) in order to obtain the desired base oil, and (d) repeating steps (a)-(c) for each base oil.

[0001] The invention is directed to a process to prepare a base oil froma waxy paraffinic Fischer-Tropsch product having a content of non-cycliciso-paraffins of more than 80 wt %.

[0002] Such a process is known from EP-A-776959. This publicationdescribes a process wherein the high boiling fraction of aFischer-Tropsch synthesis product is first hydroisomerised in thepresence of a silica/alumina supported Pd/Pt catalyst. The isomerisedproduct having a content of non-cyclic iso-paraffins of more than 80 wt% is subsequently subjected to a pour point reducing step. The disclosedpour point reducing step in one of the examples is a catalytic dewaxingstep performed in the presence of a silica-supported dealuminated ZSM-23catalyst at 310° C.

[0003] A disadvantage of such a process is that only one grade of baseoils is prepared. A next disadvantage is that the hydrosiomerisationstep is performed on a narrow boiling range fraction of aFischer-Tropsch synthesis product, which hydroisomersation step isespecially directed to prepare a base oil precursor fraction having thedesired properties. The hydroisomerisation process step can also yieldvaluable large volumes of middle distillates next to base oil precursorfractions if the feed would also include more lower boiling compounds.There is thus a desire to prepare base oils from a waxy paraffinicfraction as obtainable from a hydro-isomerisation process step, whichyields both middle distillates, such as naphtha, kerosine and gas oil,and the waxy paraffinic fraction having a content of non-cyclicparaffins of more than 80 wt %. There is also a desire to have aflexible process wherein two or more base oils having differentviscosity properties are obtained of excellent quality.

[0004] The object of the present invention is to provide a processwherein two or more high quality base oils are prepared having differentviscosities from a waxy Fischer-Tropsch product.

[0005] The following process achieves this object. Process to preparetwo or more base oil grades, which base oil grades having differentkinematic viscosities at 100° C. from a waxy paraffinic Fischer-Tropschproduct having a content of non-cyclic iso-paraffins of more than 70 wt% by

[0006] (a) obtaining from the waxy paraffinic Fischer-Tropsch product adistillate fraction having a viscosity corresponding to one of thedesired base oil products,

[0007] (b) performing a pour point reducing step using the distillatefraction obtained in step (a) as feed,

[0008] (c) optionally separating the lower boiling compounds from thedewaxed product obtained in step (b) in order to obtain the desired baseoil, and

[0009] (d) repeating steps (a)-(c) for each base oil.

[0010] Applicants found that by performing the process in the aforementioned manner a haze free base oil grade having also other excellentquality properties can be prepared. A further advantage is that in step(c) no higher boiling compounds need to be removed. Thus an energyconsuming distillation step can be omitted. The advantages are evenhigher when two or more base oils are prepared having a difference inkinematic viscosity at 100° C. of less than 2 cSt.

[0011] The waxy paraffinic Fischer-Tropsch product having the highcontent of non-cyclic iso-paraffins of more than 70 wt %, preferablymore than 80 wt %, can be obtained by well-known processes, for examplethe so-called commercial Sasol process, the Shell Middle DistillateProcess or by the non-commercial Exxon process. These and otherprocesses are for example described in more detail in EP-A-776959,EP-A-668342, U.S. Pat. No. 4,943,672, U.S. Pat. No. 5,059,299,WO-A-9934917 and WO-A-9920720. The process will generally comprise aFischer-Tropsch synthesis and a hydro-isomerisation step as described inthese publications. The hydroisomerisation step is needed to obtain therequired content of non-cyclic iso-paraffins in the feed.

[0012] In step (a) a distillate fraction having a viscositycorresponding to one of the desired base oil products is obtained fromthe waxy paraffinic Fischer-Tropsch product. Step (a) is suitablyperformed by means of distillation of a hydroisomerisation product. Thedistillation step may include a first distillation at about atmosphericconditions, preferably at a pressure of between 1.2-2 bara, whereinlower boiling fractions, for example naphtha, kerosine and gas oil areseparated from a higher boiling fraction. The higher boiling fraction,of which suitably at least 95 wt % boils above 350° C., preferably above370° C., is subsequently further separated in a vacuum distillation stepwherein a vacuum gas oil fraction, the distillate base oil precursorfraction and a higher boiling fraction are obtained. The vacuumdistillation is suitably performed at a pressure of between 0.001 and0.05 bara. When the waxy paraffinic Fischer-Tropsch product is a highboiling mixture, having an initial boiling point of between 330 and 400°C., an atmospheric distillation step may suitably be omitted.

[0013] The distillate fraction, or the distillate base oil precursorfraction as obtained in step (a), has a viscosity corresponding to thedesired viscosity of the base oil product.

[0014] For targeted base oils having a kinematic viscosity at 100° C. ofbetween 4.5 and 6 cSt the kinematic viscosity at 100° C. of thedistillate fraction is preferably between 0.05 and 0.3 cSt lower thanthe target viscosity of the base oil. More preferably the kinematicviscosity at 100° C. of the distillate fraction as obtained in step (a)is between 0.8*P and 1.2*P, wherein

P=vK@100 p−ΔPP/200.

[0015] In the above formula vK@100 p is the kinematic viscosity at 100°C. of the base oil product as to be obtained in step (c) expressed incentistokes and APP is the absolute difference in pour point of saidfraction obtained in step (a) and said product obtained in step (c) indegrees Celsius. Even more preferably said viscosity is between 0.9*Pand 1.1*P and most preferably about 1.

[0016] The kinematic viscosity at 100° C. of the distillate fraction ispreferably between 3 and 10 cSt. Suitable distillate fractions obtainedin step (a) have a T10 wt % boiling point of between 200 and 450° C. anda T90 wt % boiling point of between 300 and 650 more preferably between300 and 550° C.

[0017] In a preferred embodiment a first base oil grade having akinematic viscosity at 100° C. of between 3.5 and 4.5 cSt and a secondbase oil grade having a kinematic viscosity at 100° C. of between 4.5and 5.5 cSt are advantageously prepared in high yields by performingstep (a) in a first mode (v1) to obtain a base oil precursor fractionhaving a kinematic viscosity at 100° C. corresponding to the first baseoil grade and in a second mode (v2) to obtain a base oil precursorfraction having a kinematic viscosity at 100° C. corresponding to thesecond base oil grade. By performing the pour point reducing step (b)separately on the first and second base oil precursor fractions highquality base oils can be obtained.

[0018] In step (b) the distillate base oil precursor fraction obtainedin step (a) is subjected to a pour point reducing treatment. With a pourpoint reducing treatment is understood every process wherein the pourpoint of the base oil is reduced by more than 10° C., preferably morethan 20° C., more preferably more than 25° C.

[0019] The pour point reducing treatment can be performed by means of aso-called solvent dewaxing process or by means of a catalytic dewaxingprocess. Solvent dewaxing is well known to those skilled in the art andinvolves admixture of one or more solvents and/or wax precipitatingagents with the base oil precursor fraction and cooling the mixture to atemperature in the range of from −10° C. to −40° C., preferably in therange of from −20° C. to −35° C., to separate the wax from the oil. Theoil containing the wax is usually filtered through a filter cloth whichcan be made of textile fibres, such as cotton; porous metal cloth; orcloth made of synthetic materials. Examples of solvents which may beemployed in the solvent dewaxing process are C₃-C₆ ketones (e.g. methylethyl ketone, methyl isobutyl ketone and mixtures thereof), C₆-C₁₀aromatic hydrocarbons (e.g. toluene), mixtures of ketones and aromatics(e.g. methyl ethyl ketone and toluene), autorefrigerative solvents suchas liquefied, normally gaseous C₂-C₄ hydrocarbons such as propane,propylene, butane, butylene and mixtures thereof. Mixtures of methylethyl ketone and toluene or methyl ethyl ketone and methyl isobutylketone are generally preferred. Examples of these and other suitablesolvent dewaxing processes are described in Lubricant Base Oil and WaxProcessing, Avilino Sequeira, Jr, Marcel Dekker Inc., New York, 1994,Chapter 7.

[0020] Preferably step (b) is performed by means of a catalytic dewaxingprocess. With such a process it has been found that base oils having apour point of below −40° C. can be prepared when starting from a baseoil precursor fraction as obtained in step (a) of the present process.

[0021] The catalytic dewaxing process can be performed by any processwherein in the presence of a catalyst and hydrogen the pour point of thebase oil precursor fraction is reduced as specified above. Suitabledewaxing catalysts are heterogeneous catalysts comprising a molecularsieve and optionally in combination with a metal having a hydrogenationfunction, such as the Group VIII metals. Molecular sieves, and moresuitably intermediate pore size zeolites, have shown a good catalyticability to reduce the pour point of the distillate base oil precursorfraction under catalytic dewaxing conditions. Preferably theintermediate pore size zeolites have a pore diameter of between 0.35 and0.8 nm. Suitable intermediate pore size zeolites are ZSM-5, ZSM-12,ZSM-22, ZSM-23, SSZ-32, ZSM-35 and ZSM-48. Another preferred group ofmolecular sieves are the silica-aluminaphosphate (SAPO) materials ofwhich SAPO-11 is most preferred as for example described in U.S. Pat.No. 4,859,311. ZSM-5 may optionally be used in its HZSM-5 form in theabsence of any Group VIII metal. The other molecular sieves arepreferably used in combination with an added Group VIII metal. SuitableGroup VIII metals are nickel, cobalt, platinum and palladium. Examplesof possible combinations are Ni/ZSM-5, Pt/ZSM-23, Pd/ZSM-23, Pt/ZSM-48and Pt/SAPO-ll. Further details and examples of suitable molecularsieves and dewaxing conditions are for example described inWO-A-9718278, U.S. Pat. No. 5,053,373, U.S. Pat. No. 5,252,527 and U.S.Pat. No. 4,574,043.

[0022] The dewaxing catalyst suitably also comprises a binder. Thebinder can be a synthetic or naturally occurring (inorganic) substance,for example clay, silica and/or metal oxides. Natural occurring claysare for example of the montmorillonite and kaolin families. The binderis preferably a porous binder material, for example a refractory oxideof which examples are: alumina, silica-alumina, silica-magnesia,silica-zirconia, silica-thoria, silica-beryllia, silica-titania as wellas ternary compositions for example silica-alumina-thoria,silica-alumina-zirconia, silica-alumina-magnesia andsilica-magnesia-zirconia. More preferably a low acidity refractory oxidebinder material which is essentially free of alumina is used. Examplesof these binder materials are silica, zirconia, titanium dioxide,germanium dioxide, boria and mixtures of two or more of these of whichexamples are listed above. The most preferred binder is silica.

[0023] A preferred class of dewaxing catalysts comprise intermediatezeolite crystallites as described above and a low acidity refractoryoxide binder material which is essentially free of alumina as describedabove, wherein the surface of the aluminosilicate zeolite crystalliteshas been modified by subjecting the aluminosilicate zeolite crystallitesto a surface dealumination treatment. A preferred dealuminationtreatment is by contacting an extrudate of the binder and the zeolitewith an aqueous solution of a fluorosilicate salt as described in forexample U.S. Pat. No. 5,157,191 or WO-A-0029511. Examples of suitabledewaxing catalysts as described above are silica bound and dealuminatedPt/ZSM-5, silica bound and dealuminated Pt/ZSM-23, silica bound anddealuminated Pt/ZSM-12, silica bound and dealuminated Pt/ZSM-22 as forexample described in WO-A-0029511 and EP-B-832171.

[0024] Catalytic dewaxing conditions are known in the art and typicallyinvolve operating temperatures in the range of from 200 to 500° C.,suitably from 250 to 400° C., hydrogen pressures in the range of from 10to 200 bar, preferably from 40 to 70 bar, weight hourly space velocities(WHSV) in the range of from 0.1 to 10 kg of oil per litre of catalystper hour (kg/l/hr), suitably from 0.2 to 5 kg/l/hr, more suitably from0.5 to 3 kg/l/hr and hydrogen to oil ratios in the range of from 100 to2,000 litres of hydrogen per litre of oil. By varying the temperaturebetween 275 and suitably between 315 and 375° C. at between 40-70 bars,in the catalytic dewaxing step it is possible to prepare base oilshaving different pour point specifications varying from suitably lowerthan −60 to −10° C.

[0025] After performing a catalytic dewaxing step (b) lower boilingcompounds formed during catalytic dewaxing are removed in step (c),preferably by means of distillation, optionally in combination with aninitial flashing step.

[0026] In step (d) steps (a)-(c) are repeated for every desired baseoil.

[0027] In a preferred embodiment a first base oil (grade-4) is preparedhaving a kinematic viscosity at 100° C. of between 3.5 and 4.5 cSt(according to ASTM D 445), a volatility of below 20 wt % and preferablybelow 14 wt % (according to CEC L40 T87) and a pour point of between −15and −60° C. (according to ASTM D 97), more preferably between −25 and−60° C., by catalytic dewaxing in step (b) a distillate fractionobtained in step (a) having a kinematic viscosity at 100° C. of between3.2 and 4.4 cSt and a second base oil (grade 5) is prepared having akinematic viscosity at 100° C. of between 4.5 and 5.5, a volatility ofbelow 14 wt % and preferably below 10 wt % and a pour point of between−15 and −60° C.), more preferably between −25 and −60° C., by catalyticdewaxing in step (b) a distillate fraction obtained in step (a) having akinematic viscosity at 100° C. of between 4.2 and 5.4 cSt.

[0028]FIG. 1 shows a preferred embodiment of the process according thepresent invention. In a process (1) a waxy paraffinic Fischer-Tropschproduct (2) is prepared having a content of non-cyclic iso-paraffins ofmore than 70 wt %. From this product (2) a distillate fraction (5) isobtained in distillation column (3) by separating of a light (4) andheavy fraction (6). This fraction (5) has a viscosity which correspondswith the desired base oil grade (10). In reactor (7) a catalyticdewaxing step is performed on the fraction (5) thereby obtaining adewaxed oil (8). By separating off light fraction (9) in distillationcolumn (11) the desired base oil grade (10) is obtained. By variation ofthe separation in distillation column (3) the properties of base oilgrade (10) can be varied according to the process of the presentinvention.

[0029] The above-described Base oil grade-4 can suitably find use asbase oil for an Automatic Transmission Fluids (ATF). If the desiredkinematic viscosity at 100° C. (vK@100) of the ATF is between 3 and 3.5cSt, the Base Oil grade-4 is suitably blended with a grade having avK@100 of about 2 cSt. The base oil (grade-2) having a kinematicviscosity at 100° C. of about 2 to 3 cSt can suitably be obtained bycatalytic dewaxing of a suitable gas oil fraction as obtained in theatmospheric distillation in step (a) as described above. The AutomaticTransmission Fluid will comprise the base oil (blend) as describedabove, preferably having a vK@100 of between 3 and 6 cSt, and one ormore additives. Examples of additives are antiwear, antioxidant, andviscosity modifier additives.

[0030] The invention is furthermore directed to a novel class of baseoils having a saturates content of above 95 wt %, preferably above 97 wt%, a kinematic viscosity at 100° C. of between 8 and 12 cSt, preferablyabove 8.5 cSt and a pour point of below −30° C. and a viscosity index ofabove 120 preferably above 130. The combination of such low pour pointhigh viscosity index fluids containing almost only cyclo, normal andiso-paraffins is considered-novel. Such base oils may be advantageouslyused as white oils in medicinal or food applications. To obtain a baseoil having the desired colour specification it may be required tohydrofinish the base oil, for example using a noble metal hydrofinishingcatalyst C-624 of Criterion Catalyst Company, or by contacting the baseoil with active carbon. Base oils having a colour according to ASTM D1500 of less than 0.5 and according to ASTM D 156 Saybolt of greaterthan +10 and even equal to +30 can thus be obtained.

[0031] The base oils obtained by the present process having intermediatevK@100 values of between 2 and 9 cSt, of which preferred grade-4 andgrade-5 have been described above, are preferably used as base oil informulations such as gasoline engine oils, diesel engine oils,electrical oils or transformer oils and refrigerator oils. The use inelectrical and refrigerator oils is advantageous because of thenaturally low pour point when such a base oil, especially the gradeshaving a pour point of below −40° C., is used to blend such aformulation. This is advantageous because the highly iso-paraffinic baseoil has a naturally high resistance to oxidation compared to low pourpoint naphthenic type base oils. Especially the base oils having thevery low pour points, suitably lower than −40° C., have been found to bevery suitable for use in lubricant formulations such as gasoline anddiesel engine oils of the 0W-x specification according to the SAE J-300viscosity classification, wherein x is 20, 30, 40, 50 or 60. It has beenfound that these high tier lubricant formulations can be prepared withthe base oils obtainable by the process of the current invention. Othergasoline and diesel engine oil applications are the 5W-x and the 10W-xformulations, wherein the x is as above. The gasoline oil formulationwill suitably comprise the above-described base oil and one or more ofadditives. Examples of additive types which may form part of thecomposition are dispersants, detergents, viscosity modifying polymers,extreme pressure/antiwear additives, antioxidants, pour pointdepressants, emulsifiers, demulsifiers, corrosion inhibitors, rustinhibitors, antistaining additives, friction modifiers. Specificexamples of such additives are described in for example Kirk-OthmerEncyclopedia of Chemical Technology, third edition, volume 14, pages477-526.

[0032] The invention will be illustrated by the following non-limitingexamples.

EXAMPLE 1

[0033] 1000 g per hour of a distillate fraction of an isomerisedFischer-Tropsch product having the properties as Feed N° 1 in Table 1was fed to a catalytic dewaxing reactor. The effluent of the catalyticdewaxing reactor was topped at 390° C. to remove only the light boilingfraction. The thus obtained base oil was recovered in a 69 wt % yieldbased on Feed N° 1. The dewaxing conditions are as in Table 2. Thecatalyst used in the dewaxing step was a Pt/silica bound ZSM-5 catalystas described in Example 9 of WO-A-0029511. The properties of the thusobtained base oils are in Table 3.

EXAMPLE 2

[0034] Example 1 was repeated except at different dewaxing conditions(see Table 2). The properties of the base oil are in Table 3. TABLE 1Feed No. 1 2 Density at 70° C. 784.8 784.5 T10 wt % boiling point (° C.)407 346 T90 wt % boiling point (° C.) 520 610 Kinematic viscosity at5.151 6.244 10° C. (cSt) Pour point (° C.) +46 +30

[0035] TABLE 2 Dewaxing conditions Example 1 Example 2 Reactortemperature (° C.) 325 342 Hydrogen pressure (bar) 37 36 Weight hourlyspace 1.0 1.0 velocity (kg/l/h) Hydrogen flow rate 700 700 (Nl/h)

[0036] TABLE 3 Example 1 Example 2 Feed Feed No. 1 Feed No. 1 Base oilproperties Density at 20° C. (kg/m³) 819.7 819.0 Kinematic viscosity at5.51 5.41 100° C. (cSt) Pour Point (° C.) −20 −48 Noack (wt %) 6.3 7.4

EXAMPLE 3

[0037] Example 1 was repeated at the conditions described in Table 4using Feed No. 2 (see Table 1). The properties of the resulting base oilare presented in Table 5.

EXAMPLE 4

[0038] Example 1 was repeated at the conditions described in Table 4using Feed No. 2 (see Table 1). The properties of the resulting base oilare presented in Table 5. TABLE 4 Feed 2 Feed 2 Dewaxing conditionsExample 3 Example 4 Reactor temperature (° C.) 290 296 Hydrogen pressure(bar) 48 47 Weight hourly space 1.0 1.0 velocity (kg/l/h) Hydrogen flowrate (Nl/h) 750 750

[0039] TABLE 5 Feed 2 Feed 2 Base oil properties Example 1 Example 2Density at 20° C. (kg/m³) 826 825.9 Kinematic viscosity at 100° C. 9.789.75 (cSt) Viscosity index 151 151 Pour Point (° C.) −9 −30 Noack (wt %)6.1 6.0

[0040] The above experiments illustrate that base oils having akinematic viscosity at 100° C. in the range of 3 to 12 cSt andespecially 4 to 12 cSt having excellent properties like pour point andviscosity index can be obtained using the process according to theinvention. It will be clear that by performing step (a) and (b) in acontrolled manner according to the present invention all viscositygrades in that range can be sequentially obtained.

1. Process to prepare two or more base oil grades, which base oil gradeshaving different kinematic viscosity's at 100° C. from a waxy paraffinicFischer-Tropsch product having a content of non-cyclic iso-paraffins ofmore than 70 wt % by (a) obtaining from the waxy paraffinicFischer-Tropsch product a distillate fraction having a viscositycorresponding to one of the desired base oil products, (b) performing acatalytic dewaxing step using the distillate fraction obtained in step(a) as feed, (c) separating the lower boiling compounds from the dewaxedproduct obtained in step (b) in order to obtain the desired base oil,and (d) repeating steps (a)-(c) for each base oil.
 2. Process accordingto claim 1, wherein the waxy paraffinic Fischer-Tropsch product has acontent of non-cyclic iso-paraffins of more than 80 wt %.
 3. Processaccording to any one of claims 1-2, wherein the difference in kinematicviscosity at 100° C. of the different base oil grades is less than 2cSt.
 4. Process according to any one of claims 1-3, wherein thedistillate fraction has a T10 wt % boiling point of between 200 and 450°C. and a T90 wt % boiling point of between 300 and 550° C.
 5. Processaccording to claim 4, wherein the distillate fraction has a kinematicviscosity at 100° C. of between 3 and 10 cSt.
 6. Process according toany one of claims 1-5, wherein step (b) is performed by means of solventdewaxing.
 7. Process according to any one of claims 1-5, wherein step(b) is performed by means of catalytic dewaxing.
 8. Process according toclaim 7, wherein the catalytic dewaxing is performed in the presence ofa catalyst comprising a Group VIII metal, an intermediate pore sizezeolite having pore diameter between 0.35 and 0.8 nm, and a low acidityrefractory binder which binder is essentially free of alumina. 9.Process according to any one of claims 1-8, wherein a base oil having akinematic viscosity at 100° C. of between 4.5 and 6 cSt is prepared andwherein the kinematic viscosity at 100° C. of the distillate fraction asobtained in step (a) is between 0.8*P and 1.2*P, wherein P=vK@100p−ΔPP/200, in which equation vK@100 p is the kinematic viscosity at 100°C. of the base oil product as obtained in step (c) and APP is theabsolute difference in pour point of said fraction obtained in step (a)and said product obtained in step (c) in degrees Celsius.
 10. Processaccording to claim 9, wherein the kinematic viscosity at 100° C. of thedistillate fraction as obtained in step (a) is between 0.9*P and 1.1*P.11. Process according to claim 10, wherein the kinematic viscosity at100° C. of the distillate fraction as obtained in step (a) is aboutequal to p.
 12. Process according to any one of claims 1-11, wherein afirst base oil is prepared having a kinematic viscosity at 100° C. ofbetween 3.5 and 4.5 cSt, a volatility of below 11 wt % and a pour pointof between −15 and −60° C. by catalytic dewaxing in step (b) adistillate fraction obtained in step (a) having a kinematic viscosity at100° C. of between 3.2 and 4.4 cSt and a second base oil is preparedhaving a kinematic viscosity at 100° C. of between 4.5 and 5.5, avolatility of below 14 wt % and a pour point of between −15 and −60° C.by catalytic dewaxing in step (b) a distillate fraction obtained in step(a) having a kinematic viscosity at 100° C. of between 4.2 and 5.4 cSt.13. Passenger car motor oil comprising one of the base oils as obtainedby the process according to claim
 10. 14. Base oil having a saturatescontent of above 97 wt %, a kinematic viscosity at 100° C. of between 8and 12 cSt, a pour point of below −30° C. and a viscosity index of above120.
 15. Base oil according to claim 14, wherein the kinematic viscosityat 100° C. is higher than 8.5 cSt and the viscosity index is above 130.16. Base oil according to any one of claims 14-15, wherein the colour ofthe base oil is a colour according to ASTM D 1500 of less than 0.5 andaccording to ASTM D 156 Saybolt of between +10 and +30.
 17. Base oilaccording to any one of claims 14-16 as obtained by the processaccording to claim
 7. 18. Use of the base oil according to any one ofclaims 14-17 as a white oil in medicinal or food applications.